Galectin-3 promotes noncanonical inflammasome activation through intracellular binding to lipopolysaccharide glycans

Abstract

Cytosolic lipopolysaccharides (LPSs) bind directly to caspase-4/5/11 through their lipid A moiety, inducing inflammatory caspase oligomerization and activation, which is identified as the noncanonical inflammasome pathway. Galectins, β-galactoside–binding proteins, bind to various gram-negative bacterial LPS, which display β-galactoside–containing polysaccharide chains. Galectins are mainly present intracellularly, but their interactions with cytosolic microbial glycans have not been investigated. We report that in cell-free systems, galectin-3 augments the LPS-induced assembly of caspase-4/11 oligomers, leading to increased caspase-4/11 activation. Its carboxyl-terminal carbohydrate-recognition domain is essential for this effect, and its N-terminal domain, which contributes to the self-association property of the protein, is also critical, suggesting that this promoting effect is dependent on the functional multivalency of galectin-3. Moreover, galectin-3 enhances intracellular LPS-induced caspase-4/11 oligomerization and activation, as well as gasdermin D cleavage in human embryonic kidney (HEK) 293T cells, and it additionally promotes interleukin-1β production and pyroptotic death in macrophages. Galectin-3 also promotes caspase-11 activation and gasdermin D cleavage in macrophages treated with outer membrane vesicles, which are known to be taken up by cells and release LPSs into the cytosol. Coimmunoprecipitation confirmed that galectin-3 associates with caspase-11 after intracellular delivery of LPSs. Immunofluorescence staining revealed colocalization of LPSs, galectin-3, and caspase-11 independent of host N-glycans. Thus, we conclude that galectin-3 amplifies caspase-4/11 oligomerization and activation through LPS glycan binding, resulting in more intense pyroptosis—a critical mechanism of host resistance against bacterial infection that may provide opportunities for new therapeutic interventions.

Activation and Pharmacological Regulation of Inflammasomes

“…The K + efflux caused by GSDMD pores activates NLRP3 and initiates caspase1-dependent IL-1β and IL-18 maturation. Galectin-3 can augment caspase-4/11 oligomerization and promote non-canonical inflammasome activation through LPS binding [ 176 ]. Notably, Moretti et al unveiled another mechanism by which the simultaneous detection of bacterial RNA by NLRP3 and the binding of LPS by pro-caspase-11 promoted a pro-caspase-11–NLRP3 interaction that facilitated their interdependent activation [ 177 ].…”

Hepatic galectin-3 is associated with lipid droplet area in non-alcoholic steatohepatitis in a new swine model

“…In phase 2b, this drug was safe but not associated with significant reduction in fibrosis compared with placebo except for a subgroup of patients without oesophageal varices 67 . Since LGALS3, galectin-3, has emerged as a canonical 62 and noncanonical inflammasome activator in macrophages 68 and has been found in myeloid-derived cells 23 , it is plausible that activation LGALS3 in Kupffer cells is an early event in the cascade of events taking place in the progression from hepatic simple steatosis into NASH. However, in rats, hepatic stellate cells production of galectin-3 contributes to the expansion of hepatic progenitor cells 69 .…”

Chimeric galectin-3 and collagens: Biomarkers and potential therapeutic targets in fibroproliferative diseases

“…found that Δ1-62 and Δ1-116 showed a 3- to 6-fold increased binding efficiency to asialofetuin compared to native galectin-3 when tagged with SNAP ( 140 ). Although galectin-3 enhances neutrophil activation by binding to microbial lipopolysaccharides via its carbohydrate recognition domain, N-terminal domain is also required, indicating dependence upon multivalency of galectin-3 ( 141 , 142 ).…”